The yarn market has heretofore been looking for a high-quality, machine-spun yarn, having the feel of a natural irregularity of coarseness and fineness, thereby providing the texture and appearance of hand-spun yarn. Yarns having this irregularity in texture have been the subject of various studies.
The publication of Japanese Unexamined Patent 62-170542 discloses a spun yarn in which coarse yarn portions and fine yarn portions are mixed at random. In Japanese Unexamined Patent 62-170542, the front roller of a roller-draft type spinning frame is coupled directly to a servo motor whose speed can be freely varied by a DC voltage signal. A computer output controls the rotation of the front roller to vary it appropriately, causing the draft factor to change throughout spinning, thereby producing a yarn of random thickness.
In addition, the publication of Japanese Unexamined Patent 62-112739 discloses a spun yarn obtained by independently driving the middle roller of the draft rollers in a ring spinning frame, using a variable-speed motor, and increasing its speed at random time intervals.
Conventional machine spinning does produce a yarn with a natural, irregular feel by varying the yarn diameter at random, but this randomness produces an artificial texture with very little of the natural feel of a hand-spun yarn and the result is that it is not very comfortable for the wearer.